Wood tubing and the like



June 11, 1946.

P. GOLDMAN WOOD TUBING AND THE LIKE Original Filed Nov. 28. 1943Invw/Zor: 0 PauZB.G;0Zdman 02 W AIM 0 022%;

Patented June 11, I v x wool) TUBING AND THE LIKE Paul R. Goldman,Andover, Mass., assignor to Plymold Corporation, Lawrence, Mara, acorporate body Original application November 28, 1942, Serial- No.467,243, now Patent No. 2,352,533, dated June 27, 1944. Divided and thisapplication March 14, 1944, Serial No. 526,462

Claims. (01. 13879) 1 v 2 My present invention relates to tubes, pipeswhere a plurality of spiral wraps are provided, and other hollowcylindrical structures having each succeeding wrap is wound oppositelyto the thin wood strips and sheets as a component maone preceding, sothat the resulting plural layer terial. It aims to provide for suchstructures core element 1, such as that of Fig. 2, has its novelconstructions, arrangements and combina- 5 layers or plies individuallyalternated as to the tions of component means and elementspresentdirection of wind. ing in the resulting articles and productsdis- Thus the side-edge juncture line in any given tinctive strength andrigidity, both axially and layer crosses such line of any next adjacentlayer, radially, for a given mass and weight of the wood whether insideor outside it. Desirably also the material, and wherein the relation asbetween plies having the same direction or wind, such for flexureresistance as characterized by axial example as 8, 8b, 8d, etc., areslightly advanced strength and rigidity, on the one hand, and or setback relative to each other, with resultant crushing resistance ascharacterized by radial staggering or offsetting of their spiral jointlines. strength and rigidity, on the other hand, may The number ofwindings, plies or layers for such be predeterminedly selected andcalculated as core element 1 may be varied within a consideraappropriateto different use conditions and reble range, from a single layer upward,depending quirements. on the wall thickness desired or permissible inThis application is a division of my copending any particular instance.in the majority of cases application Serial No. 467,243, filed November28, about three to seven plies are employed, with four 1942, now Patent2,352,533, dated June 27, 1944, or five representing an averageconstruction, it containing claims directed to certain novel procbeingunderstood that the veneer strips such as esses and methods wherebytubular wood veneer 6 and 6a of Fig. 1 are representative and usuallyproducts such as here concerned may be manuare followed by'others suchas 81:, 8c, 811, Fig. 2, Iactured. these being similarly applied underalternated In the accompanying drawing, representing spiraling startingat either end of the plural ply somewhat diagrammatically a typicalembodicore I. Desirably the individual wood strips or ment of theinvention: tapes 8, 8a, etc., which may themselves be plural Fig. 1shows an initial stage of the process, ply in some instances, have thegrain or prewherein a tubing core is formed; dominant fibre directiondisposed lengthwise of Fig. 2 illustrates in cross section a typicalrethe strips, as indicated at 8g. Fig. 1, so that in suiting coreelement; the formed core 1 they extend angularly and out Fig. 3, alsorelating to the core-forming stage, of parallel to the core axis.

illustrates an example oi a pressure treatment Each such thin wood layeror wound strip 8,

01' the core; 8a, etc., as spiraliy laid on the mandrel is coated,

Figs. 4 and 5 represent an intermediate phase, either before or' inconjunction with the wrapbeing respectively an elevation of a shortlength ping. with a bonding or plastic agent, such as of the tubingunder construction and a crosscertain glues, cements or like adhesive oruniting section of the resultant intermediate structure: agents,preferably one of the polymerizableor Fig. 6 illustrates a step in afurther or third plastic type either of the cold setting or the heatphase of development of the product; and 40 setting varieties, dependingon the particular Fig. 7 is a cross-sectional view of the finished fieldof use for the tubing product in the given tubing product. instance. 4

Referring first more particularly to Figs. 1 and On completion of thewinding of the core ele- 2, the initial phase or operation in accordancement 1, pressure is applied uniformly to the enwith the inventioncomprises the formation of tire core, either before or after it isremoved an inner element or core I. For this purpose a from the mandrelM. Such pressure application removable mandrel M is'employed, of adiameter may be variously accomplished. One effective the same as theinside diameter desired for the and convenient procedure is that oftemporarilycore and for the resulting tube or pipe as a whole. wrappingthe core I with a strip or web or resil- On this mandrel there iswrapped spirally one 1 ient material 9, Fig. 3, such as a rubber orrubberor a successive plurality of layers or laminae of likecomposition, wound onto the core under tenthin wood stripping or veneer6, la, etc. Each sion proportioned to the degree of pressure desuchlayer is individually wound spirally with a sired, removabiy held at itsends as by suitable selected pitch such that the leading and trailingties or clamps, not shown.

edges of succeeding turns are abutted. Further, The cores, such as theelement l,'with the pres- 3 sure-applying means such as 9 in positionupon them are then subjected to a drying and setting or polymerizingtreatment. In the case of coldsetting binding agents this may beaccomplished by hanging or otherwise placing the tubing cores so as to.subject them to ordinary room temperatures for a period of usually 24 to48 hours, more or less. With heat-setting bonding agents the cores withthe pressure-applying means upon them may be suspended in or passedthrough a drying compartment or oven at controlled temperaturesgenerally of the range of about 180 to 240 depending on the particularagent and on the time available. In general also the polymeri-- zation,curing, drying or setting of the cores where relatively coolorcold-setting agents are employed may be considerably accelerated by aheat treatment such as referred to.

Following the drying and setting operation, wherein the compressivepressure such as afforded by the resilient means 9 is maintained, withor without the application of heat, such means is removed'from the coreelement 1, leaving the core in individually finished condition as acompact and substantially homogeneous unit in readiness for thesurrounding outer elements to be described.

It is particularly noted that by reason of the wholly spiral dispositionof any component veneer strips 8, 8a, etc., of the inner base or coreelements l, maximum advantage is taken of the compression resistingcapacity of such spirally formed structure. Resultantly these bases orcores l are of high rigidity and strength in the radial direction, thatis, against stresses acting radially and tending to crush or deformthem. It is a demonstratable fact that for a given total wall thicknessthe radial strength factor of a cylindrical structure varies with thediameter, being relatively high for the smaller diameters, anddecreasing proportionately with any increase in diameter. Hence byutilizing the inherently radially rigid spiral formation for theinnermost 01 base element Lthe one having the least internal diameter,the total resulting radial rigidity for the final tubing product ofgiven overall 'or external diameter, is proportionately increased.Otherwise stated, due to its innermost location and consequentrelatively small diameter, adequate radial rigidity is obtained with aless wall thickness and weight of component material. The result is acore or base I which is highly resistant to radial stresses but which isof relatively less rigidity in the axial direction, against forcestending to bend or deflect it or cause it to sag out of straightalignment, such as a weight or pressure intermediately applied to theelement while it is supported only at or near its ends. 1

Turning now to Figs. 4 and 5,.these represent diagrammatically a furtherand intermediate phase in the manufacture of the product, under ,theprocess of my said application Serial No.

467,243. A finished base tube or core I is itself manipulated in-themanner of a mandrel to receive upon it a longitudinally rigidiiyingelement represented as a whole by the numeral Ill. The resultantintermediate structure comprising the base i and the surrounding elementIt) will be referred to as the tubing body.

As shown in Fig. 4 byway of example, this core-surrounding element iiicomprises one or more wrappings or layers of wood veneer in sheet formwound straight onto the core I, that is, with the side edges of theveneer sheets permitdicular to the core axis. The veneer for thiscore-surrounding element l0 may be of single thickness, or it maycomprise a plurality of plies,

, two or more, three of which plies ii, Ho and lib are shown in Fig. 4by way of example, such veneer plies being bonded together either beforeor in association with their application to the core. Further, the woodmaterial for these sheets is selected and arranged so as to have thegrain or fibre extend predominately crosswise of the sheet, as indicatedat i2 in Fig. 1, that is, in or approximately in parallelism with theaxis of the core as the veneer is wound onto the latter.

Thetubing base or core I has one or more full turns or wraps of theveneer sheeting it] applied to it straightwise, that is, with astraight-on wind as above explained. As indicated diagrammatically andin an exaggerated manner at the left in Fig. 5, wherein two turns orlayers of the veneer iii are illustrated by way of example, the leadingand the terminal longitudinal edges of this veneer are disposed in closeradial proximity to each other, so that the entire resultingcoresurrounding element i0 is of uniform thickness, with no excessoverlap or part turns. The individual plies such as H, Ila, lib, Fig. 4,as also the spirally applied veneer strips 8, 8a, etc., of the tubingbase, generally have a thickness of the order of about ya to ,5 0 of aninch in the smaller sizes of tubing; that is, tubing of internaldiameters of from say A inch up to 3 or 4 inches. Hence the outwarddeflection 0r shouldering of the material of the straight-wound veneerill where it passes from one convolution to the next, as at the left inFig. 5, is but a similar small fraction of an inch in radial dimension.But by using a length of the veneer i0 precalculated to afford exactlythe desired number of winds, or by cutting it of! directly opposite theposition of its leading longitudinal edge as applied upon the core, theterminal longitudinal edge is abutted against and merged with theadjacent shallow shoulder in smooth non-thickening juncture with it.After the following pressure and setting operations the resulting jointis scarcely discernible. Prior to or during the operation of winding thecore-surrounding element Hi, it is coated at one or both faces, exceptat any externally exposed surface of the final wrap, with'a similarimpregnating and bonding agent as in connection with the formation ofthe core 1. The resulting composite tubing body composed of both thebase 1 and the surrounding element ill is then subjected to externalpressure uniformly over its outer cylindrical surface. This again may bevariously accomplished, as by temporarily winding onto it underdetermined tension a resilient pressure strip or web such as thatindicated at 9, Fig. 3, in connection with forming the core. Whilemaintaining this pressure the core-surrounding element ll of the tubingbody is cured, dried or set, with or without the application of heat,also as previously described in connection with Figs. 1 to 3. Oncompletion of the drying and setting the pressure strip or othercompressive means is removed, leaving a composite tubing body such asthat of Fig. 5 as an intermediate product.

Such composite body i-tii has a high radial. rigidity derived primarilyfrom the base i. This is eflectively augmented by the surrounding element iii. The latter, however, serves mainly to afford an axial rigidityor fiexure resistance in the resulting product of maximum efiiciencywith the given thickness and weight of the-component wood material. Thisis largely due to the do termined fact that for a given character andthickness of the wood material substantially greater longitudinal oraxial rigidity is obtained from the straight-on or convolute woundformation as illustrated in Figs. 4 and and wherein the natural grainingor fibre direction of the veneer is disposed in general parallelism withthe tubing axis. Further, such axial or fiexure-resistant strength for alaminate wood cylinder of given wall thickness increases with thediameter of the cylinder; for exampla'such tube or cylinder of say 1 in.diameter and having a wall thickness of say a in. has a higherlongitudinal rigidity, against axial fiexure, than a similarly formedtube or cylinder of say /2 in. diameter with the same wall thickness andmaterial.

Hence, in accordance with the invention, by locating thestraight-grained straight-wound veneer element in an outer position,outside the core or base 1, and thereby affording it a relatively largerdiameter, the inherent high axial rigidity factor of such element In ismade to contribute to a maximum extent toward a total axial rigidity forthe resultant wood tubing product of a given material and given insideand overall diameter, wall thickness and weight. In the resulting tubingbody such as 1-40 its two main elements thus cooperatively complementeach other to produce a structure of remarkabl high rigidity bothradially and axially, and in which each such factor is present to agreater extent than in either of the elements alone. By relativelyvarying the thickness of the respective elements 1 and ill the radialand the axial rigidity factors may be proportionately adjusted as anyparticular use circumstances may require. If desired, one or morefurther elements corresponding either tothe core I or the intermediateelement It may be-applied.

With a straight-on application of straightgrained veneer as illustratedand described in connection with Figs. 4 and 5 there is in someinstances a tendency at its outer surface for it to check or cracklengthwise of the tubing. To overcome this I complete the tubing byapplying to any external straight-laid element such as ill of thedrawing an outer covering or protective and finishing jacket such asindicated as a whole by the numeral 13 in Figs. 6 and '7. This may becomposed of one or more spiral wraps of thin wood stripping. two ofwhich are here indicated at M, Ma. The procedure for the application ofthese spirally disposed cover strips, in which the grain a preferablybut not necessarily extends mainly lengthwise the strips, may besubstantially the same as already fully described in is a. finishedsubstantially homogeneous tubing unit having hard, wear-resistantsurfaces anda high total radial and axial rigidity as above explained.

Other and continuous processes for fabricating products such as thosehereof are disclosed and claimed in the copending application of Goldmanet al., Ser. No. 488,854, filed May 28. 1943. Other tubing products tothe manufacture of which the processes of said Goldman et a1.application and 3 6 of my previously mentioned copendent Patent2,352,533 are applicable. are disclosed and claimed in my copendingapplication Ser. No. 476,690, filed February 22, 1943.

My invention is not limited to the particular embodiment as hereindescribed or illustrated, its scope being pointed out in the appendedclaims.

I claim:

1. Lamillar wood veneer tubing comprising a radially rigid core oflength-grained tape-like wood veneer strip material spirally wound inedge-abutted relation and bonded into a unitary hollow tubular element,a core-surrounding amally rigid element consisting of straight-onwrapping of veneer having its fibre direction paralleling the tube axisand being compressively bonded with itself and to the core to providewith the latter a composite tubing body, and a spirally wrapped veneerstrip covering and compressively bonded to said tubing body.

2. An integrated plywood tubing product comprising in combination alength-grained tape-like wood-veneer strip spirally wound in closededgeabutted formation both as to wind direction and grain extentpresenting a unitary radially rigid hollow tubular core, a concentriccore-surround ing axially rigid element consisting of a straightonwrapping of wood veneer formed and positioned to present its grainingpredominantly parallel to the core axis and having both longitudinalside edges closely proximateto a given radial plane-lengthwise of saidelement, said core-surrounding element having incorporated with it asynthetic resinous agent interbonding it to said core to provide withthe latter a composite tubular body, and a further spirally-wrappedtapelike wood-veneer strip covering and-bonded to' said body to presenttherewith the integrated tubing product.

3. Rigid hollow tubing having concentric continuous smooth-walled innerand outer surfaces.

said tubing formed of wood veneer stripping and comprising a spirallydisposed edge-abutted winding of said stripping defining'a core, anintermediate wood veneer layer of circumferentially uniform thicknessconvolutely surrounding said core with the grain paralleling its axis,and an outer spiralled edge-abutted winding of said veneer strippingcovering said intermediate layer, each winding and layer beingresin-bonded to that next adjacent and together presenting an integratedsubstantially homogeneous unitary product of predetermined radial andaxial strength and rigidity for the given total wall thickness.

4. A substantially rigid hollow tubing structure comprising a series oftape-like length-grained veneer strips wound spirally one on anotheralternately in opposite directions each in edge-abutted relation andbearing between winds a polymerized plastic bonding agent consolidatingthem into a dense-walled radially rigid hollow base unit, apredominantly transversely grained veneer web wound straight onto saidbase unit convolutely with the graining lengthwise the latter, said webapplied to a uniform thickness of wind about the entire circumference ofthe base unit with its leading and trailing longitudinal side edgesedges terminated closely proximate to the same radial plane lengthwiseof the unit and beingsimsaid tubing body.

5. An integrated plywood tubing product comprising in combination aseries 01 length-grained tape-like wood-veneer strips respectively woundin alternately opposite directions in closed edgeabutted spiralformation both as to wind direction and grain extent and having betweensuccessive strips a synthetic resinous agent bonding them into a unitaryradially rigid hollow tubular core, a concentric core-surroundingaxially rigid element consisting of a straight-on wrapping oi. woodveneer formed and positioned to present its graining predominantlyparallel to the core veriang and similarly bonded to said body to

